The present disclosure relates to a fixing device fixing a toner image on a recording medium and an image forming apparatus including the fixing device.
An electrographic image forming apparatus, such as a printer or a copying machine, forms a toner image on a surface of a recording medium, such as a sheet, and then, heats and pressures the recording medium and toner image by a fixing device, thereby fixing the toner image on the recording medium.
As a manner applied in the above-mentioned fixing device, a manner forming a fixing nip heating and pressuring the recording medium and toner image by a fixing roller and a pressuring roller is known. The above-mentioned fixing roller is formed, for example, by covering the outer circumference face of a cored bar made of metal by a resin having high toner releasability. As a heat source heating the above-mentioned fixing roller, for example, a halogen heater is used. The halogen heater is arranged, for example, inside the cored bar of the fixing roller.
On the other hand, another manner (so-called as an “IH (Induction Heating) manner”) using an IH coil as the heat source instead of the halogen heater is known. The above-mentioned IH coil produces magnetic field by conducting electricity. In such an IH manner-type fixing device, instead of forming the fixing nip by the fixing roller and pressuring roller, the fixing nip is often formed by a fixing belt and the pressuring roller. The above-mentioned fixing belt is made of a rotatable endless belt. The magnetic field produced by the above-mentioned IH coil acts on the fixing belt so as to produce eddy current, thereby generating heat in the fixing belt.
As a rotating manner of the fixing belt, a manner rotating the fixing belt together with one or more rollers arranged at an internal diameter side of the fixing belt is known. On the other hand, another manner sliding the fixing belt with respect to a pressuring member arranged at the internal diameter side of the fixing belt is also known.
In the fixing device with such a manner, the fixing belt may be biased to one side in a rotation axis direction due to a gap of alignment of components of the fixing device, variation of temperature in the fixing device or other cause. Restriction of such a bias of the fixing belt is one of important tasks.
As a configuration achieving such an task, there is a configuration suppressing the bias of the fixing belt by holding an end part of the fixing belt by a resin member (e.g., a resin cap or a resin ring) and restricting movement of the above-mentioned resin member in the rotation axis direction of the fixing belt. However, if such a configuration is applied, there are possibilities that, since the end part of the fixing belt and resin member are rubbed, a crack in the end part of the fixing belt is caused and the resin member is scraped.
By contrast, there is a fixing device including a cap member attached to the end part of the fixing belt and an elastic member interposed between the fixing belt and cap member.
A first problem of the fixing device having such a configuration will be explained with reference to FIG. 10. In a configuration as shown in FIG. 10, a part of the cap member 102 is inserted into an internal diameter side of the fixing belt 101, and then, the elastic member 103 is interposed between the fixing belt 101 and cap member 102. In such a configuration, if deformation of the fixing belt 101 to the internal diameter side is attempted according to pressure (refer to an arrow a in FIG. 10) from the pressuring roller, the fixing belt 101 is not deformed more than a pressure deformation amount (refer to an arrow b in FIG. 10) of the elastic member 103. Therefore, it is difficult to respond to a case where great deformation of the fixing belt 101 to the internal diameter side is desired, i.e., a case where widening of width of the fixing nip is desired.
Next, a second problem of the fixing device having the above-mentioned configuration will be explained with reference to FIG. 11. In the configuration shown in FIG. 11, an external diameter side of the fixing belt 101 is covered by a part of the cap member 102 and the elastic member 103 is interposed between the fixing belt 101 and cap member 102. If such a configuration is applied, since the deformation of the fixing belt 101 to the internal diameter side is not restricted, the pressure deformation amount of the fixing belt 101 may be sufficiently secured.
However, biased force (refer to an arrow c in FIG. 11) to one side in the rotation axis direction is added to the fixing belt 101, and then, the elastic member 103 is pressured to the cap member 102 by this force. Therefore, when the fixing belt 101 after passing through the fixing nip is restored to the external diameter side, a catch occurs in a contact part (refer to an area surrounded by a circle d in FIG. 11) of the cap member 102 and elastic member 103 and the restoration of the fixing belt 101 to the external diameter side is obstructed.